"If you use the internet, you're the subject of hundreds of experiments at any given time, on every site," it said. "That's how websites work."

OKCupid said one revelation was that "people just look at the picture".

As well as allowing users to upload pictures and set up dating profiles, OKCupid asks users questions and matches them with potential partners based on the answers.

In one experiment, the site took pairs of "bad" matches between two people - about 30% - and told them they were "exceptionally good" for each other, or 90% matches. "Not surprisingly, the users sent more first messages when we said they were compatible," Christian Rudder, one of the founders of OKCupid, said in a blog post on the company's research and insights blog.

Further experiments suggested that "when we tell people they are a good match, they act as if they are. Even when they should be wrong for each other." The company later revealed the correct scores to the participants.

"This shows how easy it is for a company to put at risk the trust that users place in them," Daniel Tozer, a commercial technology partner at the law firm Harbottle and Lewis, told the BBC. "There are data protection issues when you're using users' personal information, especially when it appears OKCupid are actually changing things on the page.

"If you're doing anything extremely unusual with people's data, and I would argue this is the case here, it's always best to seek the consent of your users first."

'Words worth nothing'

In another experiment, OKCupid ran profiles with pictures and no profile text for half of its test subjects, and vice versa for the rest. The results showed that people responded solely to the pictures. For potential daters, Mr Rudder said that "your actual words are worth… almost nothing".

The revelations come as a result of Facebook saying that in late June, it changed some "news feeds to control which emotional expressions the users were exposed to" as part of research in collaboration with two US universities.

The research was conducted on 689,000 Facebook users over a period of one week in 2012.

Many users and observers felt the actions were unethical. In the US, Senator Mark Warner asked the regulator, the Federal Trade Commission, to look into the issue, while a Labour MP in the UK called for an investigation.

OKCupid said that experiments like the ones that it and Facebook ran are part and parcel of creating websites. "It's not like people have been building these things for very long, or you can go look up a blueprint or something," Mr Rudder said. "Most ideas are bad. Even good ideas could be better. Experiments are how you sort all this out."

BBC links

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